Enantiospecific synthesis of (S)-(−)-8-oxoxylopinine

The enantiospecific synthesis of ( S )-(−)-8-oxoxylopinine 1 was performed using a lateral metallation strategy, in which ( S )-alaninol or ( S )-phenylalaninol was applied as chiral auxiliary and building block. (4 S )-3-(4,5-Dimethoxy-2-methylbenzoyl)-2,2,4-trimethyl-1,3-oxazolidine 12 was synthesized starting from veratraldehyde 13 . The addition reaction of benzylic anion generated in situ from chiral amide 12 into 6,7,-dimethoxy-3,4-dihydroisoquinoline 7a proceeded with simultaneous cyclization leading to the protoberberine alkaloid with high enantioselectivity.